In recent years it has become possible to manufacture semiconductor structures in which the mobile charge carriers (typically electrons) are confined to a region whose extent in one dimension is so limited that the mobile charge carriers can be considered a 2-dimensional electron gas (2 DEG). For a discussion of 2 DEG see, for instance, H. L. Stormer, Surface Science, Vol. 132(1-3) pp. 519-526.
B. J. van Wees, et al., Physical Review Letters, Vol. 60(9), pp. 848-850 (1988), have studied ballistic point contacts, defined in the 2 DEG of a GaAsAlGaAs heterostructure. The point contact is defined by electrostatic depletion of the 2 DEG underneath a gate formed by means of an appropriately patterned metallization layer on the semiconductor heterostructure. By varying the voltage applied to the gate the effective width of the point contact could be varied. H. van Houten, et al., Europhysics Letters, Vol. 5(8), pp. 721-725 (1988) reported electron focusing in a 2 DEG by means of a magnetic field. And G. H. Bernstein, et al., Annual Report, College of Engineering and Applied Sciences, Arizona State University, pp. 24-25, Jul. 1, 1988, have proposed an "electron diffraction transistor" which comprises a split gate and a multiplicity of angularly spaced drain "fingers". Simulation is reported to show that such a device can exhibit finger-to-finger variations in current that oscillate with angle, and corresponding fixed angle currents that oscillate with gate voltage.